This application relates to compositions of amorphous metallic materials and bulk metallic glasses (BMGs).
Amorphous metallic materials made of multiple components are amorphous with a non-crystalline structure and are also known as “metallic glass” materials. Such materials are very different in structure and behavior from many metallic materials with crystalline structures. Notably, an amorphous metallic material is usually stronger than a crystalline alloy of the same or similar composition. Bulk metallic glasses are a specific type of amorphous materials or metallic glass made directly from the liquid state without any crystalline phase. Bulk metallic glasses exhibit slow critical cooling rates, e.g., less than 100 K/s, high material strength and high resistance to corrosion.
Bulk metallic glasses may be produced by various processes, e.g., rapid solidification of molten alloys at a rate that the atoms of the multiple components do not have sufficient time to align and form crystalline structures. Alloys with high amorphous formability can be cooled at slower rates and thus be made into larger volumes. The amorphous formability of an alloy can be described by its thermal characteristics. One such thermal characteristic is the reduced glass transition temperature, defined as the ratio between the glass transition temperature and the melting temperature. Another thermal characteristic of a bulk metallic glass is the supercooled liquid range, defined as the difference between the glass transition temperature and the crystallization temperature. Amorphous formability increases when the reduced glass temperature decreases, and when the supercooled liquid range increases.
Various known iron-based amorphous alloy compositions suitable for making non-bulk metallic glasses) have relatively limited amorphous formability and are used for various applications, such as transformers, sensor applications, and magnetic recording heads and devices. These and other applications have limited demands on the sizes and volumes of the amorphous alloys, which need to be produced. By contrast, bulk metallic glasses can be formulated to be fabricated at slower critical cooling rates, allowing thicker sections or more complex shapes to be formed. These Fe-based BMGs can have strength and hardness far exceeding conventional high strength materials with crystalline structures and thus can be used as structural materials in applications that demand high strength and hardness or enhanced formability.
Some iron-based bulk metallic glasses have been made using iron concentrations ranging from 50 to 70 atomic percent. Metalloid elements, such as carbon, boron, or phosphorous, have been used in combination with refractory metals to form bulk amorphous alloys. The alloys can be produced into volumes ranging from millimeter sized sheets or cylinders. A reduced glass transition temperature on the order of 0.6 and a supercooled liquid region greater than approximately 20K indicates high amorphous formability in Fe-based alloys.